1. Field of the Invention
The invention relates to a fuel injection device for shaping a flexible injection pressure curve, with which on the one hand, a high degree of freedom can be achieved with regard to the construction and design of an injection system for highly pressurized fuel and on the other hand, the injection pressure curves can be adapted to an extremely wide range of operating conditions of an injection system. Current fuel injection system designs generally strive to reduce the number of moving components and therefore also to reduce the overall number of parts.
2. Prior Art
EP-0-823-549-A2 and EP-0-823-550-A1 have disclosed devices for injecting highly pressurized fuel into the combustion chambers of internal combustion engines, in which either a variable nozzle opening pressure can be set or a pressure increase phase (boot phase) can be produced that precedes the main injection phase. The outflow of fuel from a nozzle needle control chamber is controlled in order to adjust a variable nozzle opening pressure in the fuel injector; solenoid valves are used in these embodiments. In the embodiments known from the prior art, the solenoid valves are disposed above the control valves and consequently increase the overall height of the fuel injector. This translates into additional restrictions in the construction and installation of these valves in internal combustion engines, which must be taken into account in order to assure a proper function of the injection system.
Since the variable nozzle opening pressure in the injector disclosed by EP-0-823-550-A1 is achieved by means of the outflow of a control volume from the nozzle needle control chamber, consideration must be given to the fact that in this embodiment from the prior art, intermediary positions of the control valves that control the pressurization only change slowly and shorter switching times can only be achieved with difficulty; these shorter switching times, however, are very important in fuel injection systems, particularly at higher engine speeds.